1. Field of the Invention
This invention is directed to catheters adapted for long term implantation within living bodies and characterized by non-adherent contacting polymer surfaces. In some catheter designs, polymer films are in close contact with polymer surfaces. Two catheters of this type are disclosed in the copending Dorman application Ser. No. 245,379, filed Mar. 19, 1981, and the copending Wigness et al application Ser. No. 367,683, filed Apr. 12, 1982, hereafter referred to as the check valve catheter and the vascular access catheter, respectively. Both applications are of common ownership with the present application.
The preferred form of the check valve catheter consists of a thin silicone rubber sleeve stretched over a silicone rubber catheter. Silicone rubber surfaces in contact will adhere over time. This can result from the attraction of some compounds to chemically similar compounds and a knitting phenomenon where loose polymer chains at the surface become woven together. This adhesion greatly compromises the long term operation of the check valve catheter. During its development, a method of eliminating this adhesion was researched. A method of impregnating the rubber with a lubricant gave a temporary solution, but a permanent solid lubricant that would not leach out was desired. Films of graphite and albumin were sandwiched between the sleeve and the catheter but did not reduce adhesion significantly. Although silicone rubber has a low surface energy which is known to reduce adhesion, its ability to knit into a surface increases the actual surface contact causing a net increase of adhesion. For these reasons, a smooth film of lower surface energy than silicone rubber was desired.
The vascular access catheter consists of a flexible partition inside the catheter that can be shifted to one side to expose an inner lumen, thus enabling blood withdrawal or infusion. In its preferred form, it is made of silicone rubber and over time the contacting surfaces adhere to one another.
A fluorocarbon surface, such as polytetrafluoroethylene (PTFE) is known to have the desired nonadhering qualities. Glow discharge plasma polymerization of fluorocarbons is the only method known to provide the conditions necessary to react fluorine groups with the inert methyl groups on the surface of silicone rubber.
2. The Prior Art
Plasma polymerization of TFE has been widely studied in the last decade. Although most of the studies are aimed at understanding the process, a few specific applications have been cited and patents that include the process have been granted. U.S. Pat. No. 4,125,152, granted on Nov. 14, 1978, discloses the use of plasma polymerization of TFE to prevent adherent scale deposition on heat transfer surfaces in contact with heat transfer fluids. U.S. Pat. No. 4,100,113, granted on July 11, 1978, discloses the use of plasma polymerization of TFE in the preparation of electrolytic cell membranes by polymerization onto polymer substrates.
U.S. Pat. No. 3,703,585, granted on Nov. 21, 1972, discloses a process of sputtering PTFE polymer onto a substrate. This process differs from plasma polymerization of TFE in that a glow discharge using an inert gas such as argon is used to break off free radicals from the base material. The radicals are then able to deposit onto a substrate. This process has been studied for applying lubricant to small parts (K. G. Budinski, J. Vac. Sci. Technol. 12:786-789, 1975).